title: Mechanisms of abnormal systolic motion of the interventricular septum during left bundle-branch block.
abstract: BACKGROUND
  In a majority of patients with left bundle-branch block (LBBB), there is abnormal leftward motion of the interventricular septum during the preejection phase. This motion was considered to be passive, caused by early rise in right ventricular (RV) pressure, and has therefore been excluded from most indices of left ventricular (LV) dyssynchrony. If considered active, however, the leftward motion reflects onset of septal activation and should be included. We therefore investigated if the motion was a passive response to pressure changes or caused by active contraction.
  
  
  RESULTS
  LBBB was induced in 8 anesthetized dogs with micromanometers. Cardiac dimensions were measured by sonomicrometry and echocardiography. Induction of LBBB resulted in preejection leftward motion of the septum, simultaneously with shortening of septal segments (P<0.01). In each experiment, preejection septal shortening occurred against rising LV pressure, consistent with active contraction. Furthermore, the LV pressure-segment length relationships were shifted upward (P<0.01) relative to the passive elastic curve, indicating stiffening of septal myocardium, confirming an active mechanism. Initially, RV pressure increased faster than LV pressure, suggesting that the leftward septal motion may have a passive pressure component. However, the passive component appeared to play a minor role. The magnitude of preejection septal shortening was modified by load alterations.
  
  
  CONCLUSIONS
  Leftward preejection motion of the septum during LBBB is mainly a result of active septal contraction, whereas alterations in diastolic ventricular pressures modulate the amplitude of this motion. The findings imply that the preejection phase should be included when assessing LV dyssynchrony.
authors.affiliation: Institute for Surgical Research and Department of Cardiology, Oslo University Hospital, Rikshospitalet, and University of Oslo, Oslo, Norway.
authors.forename: Ola
authors.initials: O
authors.lastname: Gjesdal
authors.forename: Espen W
authors.initials: EW
authors.lastname: Remme
authors.forename: Anders
authors.initials: A
authors.lastname: Opdahl
authors.forename: Helge
authors.initials: H
authors.lastname: Skulstad
authors.forename: Kristoffer
authors.initials: K
authors.lastname: Russell
authors.forename: Erik
authors.initials: E
authors.lastname: Kongsgaard
authors.forename: Thor
authors.initials: T
authors.lastname: Edvardsen
authors.forename: Otto A
authors.initials: OA
authors.lastname: Smiseth
mesh_terms: D000818:Animals; D002037:Bundle-Branch Block / Q000000981:diagnostic imaging / Q000503:physiopathology*; D004285:Dogs; D004452:Echocardiography; D004562:Electrocardiography; D006439:Hemodynamics; D009200:Myocardial Contraction; D013599:Systole; D016277:Ventricular Function, Left; D017725:Ventricular Pressure; D054088:Ventricular Septum / Q000503:physiopathology*